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VertebraEdit

Vertebrae are the bony building blocks of the backbone, forming the central axis of the skeleton. In humans, the vertebral column is a durable, flexible framework that bears the head and torso, protects the spinal cord, and provides attachment points for muscles and ligaments. The adult spine typically comprises 33 vertebrae, though four or five segments may fuse in the sacrum and coccyx during development. The movable portion includes the 7 cervical, 12 thoracic, and 5 lumbar vertebrae, with the sacrum and coccyx constituting the fused remnants of what were once separate bones. Each vertebra contributes to a column that balances stability and mobility, and the entire sequence is interwoven with intervertebral discs, nerves, and connective tissue that coordinate movement, sensation, and posture.

The study of vertebrae encompasses their anatomy, regional variation, development, and clinical significance. Understanding how a single vertebra fits into the broader Vertebral column helps explain how the spine supports the body, protects the Spinal cord, and accommodates a wide range of motions while remaining resilient under load. For a broader context on the structure that houses these bones, see Vertebral column.

Anatomy

A typical vertebra consists of a anterior weight-bearing body and a posterior arch that together enclose the Vertebral foramen, a passage through which the spinal cord travels. The arch is composed of two main parts: the Pedicles, which connect the body to the posterior elements, and the Laminae, which complete the posterior wall. Extending from the arch are several processes that give attachment points to muscles and ligaments: the Spinous process projects posteriorly, while the paired Transverse processes project laterally. The articular surfaces form the Facet joints (zygapophysial joints) with adjacent vertebrae, guiding and restricting motion.

The central body of the vertebra is a roughly cylindrical mass of cortical bone surrounding a cancellous core. The body bears most of the axial load and articulates with the adjacent vertebrae via the Intervertebral disc that sits between successive bodies. Endplates at the top and bottom of the body interface with the disc material, influencing nutrient exchange and disc health.

Housed within the vertebral arch is the Vertebral foramen. When vertebrae are stacked, the foramina align to create the Spinal canal, which encases and protects the Spinal cord and the roots of the spinal nerves. The space available for the spinal cord is modulated by the size and shape of the vertebrae and by pathological changes such as degenerative disease or fracture.

Regions of the spine exhibit notable differences. The cervical vertebrae include features that accommodate head mobility and arterial passage, such as the foramen transversarium and, in the upper cervical vertebrae, the specialized shapes of the atlas (C1) and axis (C2). The thoracic vertebrae bear facets for rib articulation on the bodies and the transverse processes, linking the spine to the rib cage. The lumbar vertebrae are large and robust, designed for substantial weight-bearing and lifting tasks, with relatively thick bodies and a more reduced range of motion compared with the cervical region.

Key anatomical terms and their roles include: - Vertebral body: the anterior, weight-bearing portion. - Vertebral arch: the posterior part that forms the protective enclosure around the spinal canal. - Vertebral foramen: the opening through which the spinal cord passes. - Spinous process and Transverse process: attachment points for muscles and ligaments. - Facet joint: the synovial joints between vertebrae that guide motion. - Intervertebral disc: the fibrocartilaginous cushion between bodies; composed of the Annulus fibrosus and the Nucleus pulposus. - Vertebral artery pathways in the cervical region via the foramen transversarium. - Intervertebral foramina: openings for exiting spinal nerves.

Discs are a central feature of vertebral function. The Annulus fibrosus is a tough outer ring that contains the softer Nucleus pulposus, which acts as a cushion and distributes load. Together, these discs enable flexibility and shock absorption between rigid vertebrae.

Region-specific features include: - Cervical vertebrae (C1–C7): wider range of motion, presence of a lateral mass and foramina transversaria in most levels, and distinctive atlas (C1) and axis (C2) structures, which allow nodding and rotation of the head. - Thoracic vertebrae (T1–T12): attachment points for ribs; costal facets on the bodies and transverse processes; a more restrictive range of motion suitable for supporting the thoracic cage. - Lumbar vertebrae (L1–L5): large, robust bodies designed for weight-bearing; increased anterior-posterior size and facets oriented to limit rotation.

The spine’s orientation and curvature are essential for distributing mechanical stress. The normal adult spine exhibits curves in the sagittal plane: a lordosis in the cervical and lumbar regions and a kyphosis in the thoracic region. These curvatures contribute to balance, shock absorption, and the mechanical efficiency of standing and walking. The terms and mechanisms of these curvatures are covered in discussions of Spine biomechanics and Posture.

Development and variation

Vertebral formation begins early in embryonic development. The axial skeleton arises from somites, segmented blocks of mesoderm, which differentiate into the Sclerotome portion to form the vertebral bodies and arches. The process involves segments of cartilage that later ossify through a combination of primary and secondary ossification centers, giving rise to the mature vertebrae. The development and segmentation of the Vertebral column are topics within Embryology and Skeletal development.

Variations in vertebral anatomy are common. Some individuals have extra ribs or transitional vertebrae at the thoracolumbar junction, which can influence biomechanics or risk for certain conditions. The spine is also subject to degenerative changes with age, most notably in the discs and facet joints, and it can be affected by conditions such as osteoporosis that compromise bone density and strength. See discussions of Osteoporosis and Degenerative disc disease for further context.

In the broader taxonomic sense, vertebrae evolved as part of the axial skeleton in early vertebrates, with specialization in different lineages leading to the diverse forms seen across animals. For comparative anatomy, see entries on Vertebrate anatomy and Vertebra across taxa.

Function and health

The vertebral column serves several interdependent roles: - Support for the head and trunk, enabling upright posture and weight transfer to the pelvis. - Protection of the spinal cord within the Spinal canal, as well as protection for the origins of the spinal nerves emerging through the Intervertebral foramina. - Facilitation of movement through articulated joints and discs that permit bending, twisting, and guided rotation. - Attachment points for muscles, ligaments, and tendons that coordinate movement and stabilize the trunk.

Clinical issues involving the vertebrae and their associated structures are a major focus of medical practice. Common concerns include: - Fractures of vertebral bodies or arches, which can result from trauma or osteoporosis and may threaten spinal stability or nerve function. See Vertebral fracture for more detail. - Intervertebral disc herniation or degenerative disc disease, which can compress nerve roots and cause pain or neurologic symptoms. See Intervertebral disc herniation and Osteoarthritis of the spine. - Degenerative changes of the facet joints and ligaments leading to spinal stenosis or reduced mobility, sometimes requiring imaging with Magnetic resonance imaging or Computed tomography and, in severe cases, surgical intervention. - Postural and alignment issues such as scoliosis, lordosis, or kyphosis, which may require evaluation in the context of Spinal deformity and rehabilitation approaches.

Imaging and evaluation of the vertebrae typically involve modalities such as X-ray, MRI, and CT, often interpreted in the context of the adjacent soft tissues and neural structures. See Radiology and Neuroimaging for those topics.

See also